1. Field of the Invention
The present invention is concerned with the manufacture of pure quartz glass and relates in particular to the production of a product suitable for producing such pure quartz glass, from types of quartz which have been considered unsuitable for producing pure quartz glass up to now. The invention further relates to the use of the product obtained from such types of quartz according to the invention, for growing piezoelectric crystals.
2. Description of the Prior Art
Ever since quartz was first industrially processed into quartz glass (flint glass) around the turn of the century, crude quartz has been used for this purpose, which was selected from the various deposits according solely to the criterion that it be more or less clear as water but at least transparent.
The quartz glass melted from this raw material was more or less clear as water or at least transparent, also depending on the particular way the method is carried out.
By improving the melting and processing techniques, the transparency and optical behavior of quartz glass melted from crude quartz which was not quite clear as water but only transparent, could be adapted to the properties of quartz glass melted from crude quartz which was clear as water, for example by minimizing the bubble content, homogenization, etc.
It has become increasingly necessary to search for an improvement in the process techniques because the reserves of crude quartz which is clear as water do not suffice to meet the growing demand.
In the known methods for melting quartz glass, the at least transparent crude quartz obtained is broken into pieces of up to approx. 100 g, heated above the alpha-beta transformation point of the quartz of 573.degree. C. and then quenched in soft, demineralized or deionized water.
The extremely pure product thus obtained is then ground down to a grain of less than approx. 1 mm in an agate mill or by means of grinding tools with similarly unproblematic abrasion, sifted, fractionated and possibly subjected to mechanical and/or chemical final cleaning in order to eliminate certain superficial contamination which has come into the product during the reducing process. This product can be melted, for example, in a crucible. A shaped body may be removed from the melt. But the product may also be ground further to an even smaller grain size and then introduced into a gas or plasma burner from which, contained in the flame, it hits a catching body on which a quartz glass body builds up.
There is also a known method (IMC-Spruce-Pine, N.C.) in which pegmatite, because of the feldspar, is processed to a floatable grain &lt;300 .mu.m using customary crushing and grinding tools and the quartz contained in the pegmatite is processed using a combination of mechanical and chemical means to form a raw material which is suitable for customary, but not for higher-quality, quartz glass products. For the extremely pure raw material is contaminated in an undesirable fashion in this method both by flotation residue and by the abrasion of the reducing tools, so that it cannot be used for a large number of applications, in particular for use in optics, in semiconductor technology, in communication engineering (optical fibers) and in the lamp industry.
The demand for quartz glass which has greatly increased in the last ten years or so for a growing number of applications, such as the lighting industry, the semiconductor industry, communication engineering, smelting plants, chemical engineering and optics, confronts the suppliers of crude quartz with problems which can hardly be solved. It is to be expected that the reserves of crude quartz which is clear as water or transparent will shortly no longer meet the constantly increasing demand of the producers of quartz glass. The large reserves of quartz which is not transparent (milky quartz) which do exist have not been exploited for the processing of quartz glass up to now because most of this non-transparent quartz is so contaminated by nature that quartz glass obtained therefrom cannot be used for any subsequent application.